feat: no VoidValue, just Void type

include/ir/ir.hpp

@@ -54,7 +54,7 @@ namespace IR
                 argRegs.Push(arg);
             }
             // TODO: gather return type of the function
-            auto dst = VoidValue();
+            auto dst = AllocateNamed<Instruction>(new ValueHandle::Type {ValueHandle::Type::Kind::Void});
             m_ops->Push(new CallOp(dst, fn->name(), argRegs.view()));
             return dst;
         }
@@ -75,7 +75,7 @@ namespace IR
             }
 
             assert(0 && "unreachable");
-            return reinterpret_cast<ValueHandle *>(new Void());
+            return nullptr;
         }
 
         ValueHandle *ParseExpression(const Node *expression)
@@ -187,11 +187,6 @@ namespace IR
             return new V(ValueHandle::kNoId, std::forward<Args>(args)...);
         }
 
-        ValueHandle *VoidValue()
-        {
-            return new Void();
-        }
-
     private:
         const Node *m_root = nullptr;